1. Field of the Invention
The present invention relates generally to an alternator mounted on a vehicle such as a passenger car, a truck or the like, and more particularly to an alternator with a rectifier for rectifying an alternating current generated in the alternator.
2. Description of Related Art
A slant nose type vehicle has recently been required to decrease a running resistance in a vehicle and to improve a field of vision for a driver. Further, a wide accommodation space of a vehicle compartment has recently been required to give better comfort to occupants of the vehicle. These requirements narrow an engine room space. In addition, the number of members disposed around an engine of the vehicle has been increased. Therefore, an alternator is inevitably disposed near the engine, so that heat received in the alternator from the engine has been increased. Further, the alternator is required to be made in a smaller size.
Further, because the number of current consumers has been increased to improve comfort and safety to the occupants, the alternator is required to generate a larger electrical energy. Therefore, heat generated in the alternator itself has been increased. Particularly, a rectifier having many diodes generates a large amount of heat. Therefore, it is required to improve a cooling performance of the rectifier disposed in a narrow space at a low cost. Each diode of the rectifier has a semiconductor pellet and a disk electrically connected with each other. To dissipate heat generated in the semiconductor pellets to the atmosphere, the disks of the rectifier are attached to a heat sink by soldering.
Further, to prevent thermal fatigue caused in the solder during the disk attachment, Published Japanese Patent First Publication No. 2002-119029 discloses an alternator wherein disks of rectifying elements (or diodes) of a rectifier are pressed into holes opened in a heat sink to fix the rectifying elements to the heat sink. In this alternator, the disks are formed of a material having a hardness higher than that of the heat sink. Therefore, the disks are hardly deformed when being inserted into the holes, and stresses of the disks on semiconductor pellets are reduced. Further, in this rectifier, the thickness of each disk is set to be equal to or larger than that of the heat sink to place the semiconductor pellet away from a side surface of the disk being in contact with the heat sink. With this structure, when the disk is pressed into a hole of the heat sink, a compressive stress added to the semiconductor pellet is considerably reduced.
However, holes in the heat sink are formed by the deformation processing such as press processing. In this case, a size of each hole cannot be precisely set, so that an allowance between the hole and disk becomes insufficient. Further, hardness at portions of the heat sink surrounding the holes is heightened by the deformation processing, so that it is difficult to sufficiently reduce stress on the semiconductor pellet when the disk is pressed into the hole. Further, when the disk is thickened so as to place the semiconductor pellet further away from a surface of the disk being contact with the heat sink, each rectifying element becomes large in a thickness direction. Therefore, the rectifier cannot be downsized.
Further, Published Japanese Patent First Publication No. 2004-112860 discloses an alternator wherein a plurality of sub-fins are formed in a complicate structure by deforming an aluminum plate by die casting and are attached to a heat sink to stand on the heat sink. Therefore, a heat dissipating area of the heat sink becomes large, so that a cooling performance of the rectifier can be improved without enlarging the heat sink along its extending direction.
However, although the sub-fins deformed by die casting can be arbitrarily shaped to heighten the cooling performance of the rectifier, surface portions of the sub-fins are hardened due to the casting. In this case, when the disks are pressed into the holes of the heat sink, it is sometimes difficult to reduce a stress on the semiconductor pellets.